Hybrid variation-perturbation method for calculating rovibrational energy levels of polyatomic molecules

摘要: A procedure for calculation of rotation-vibration states medium sized molecules is presented. It combines the advantages variational calculations and perturbation theory. The vibrational problem solved by diagonalizing a Hamiltonian matrix, which partitioned into two sub-blocks. first, smaller sub-block includes matrix elements with largest contribution to energy levels targeted in calculations. second, larger comprises those basis have little effect on these levels. Numerical theory, implemented as Jacobi rotation, used compute contributions from second sub-block. Only first needs be stored memory diagonalized. Calculations vibrational-rotational also employ partitioning sub-blocks, each corresponds either single state or set resonating states, all associated rotational Physically, this efficient when Coriolis coupling between different small. theory include cross-contributions states. Separate individual sub-blocks are then diagonalized, replacing diagonalization large number small diagonalizations. examples show that proposed hybrid variational-perturbation method greatly speeds up without significant loss precision both transition intensities. scheme can accurate nuclear motion 15 atoms currently available computers.